// SPDX-License-Identifier: GPL-2.0 #include #include #include #include #include #include #include "kcsan.h" #include "encoding.h" /* * Max. number of stack entries to show in the report. */ #define NUM_STACK_ENTRIES 64 /* * Other thread info: communicated from other racing thread to thread that set * up the watchpoint, which then prints the complete report atomically. Only * need one struct, as all threads should to be serialized regardless to print * the reports, with reporting being in the slow-path. */ static struct { const volatile void *ptr; size_t size; bool is_write; int task_pid; int cpu_id; unsigned long stack_entries[NUM_STACK_ENTRIES]; int num_stack_entries; } other_info = { .ptr = NULL }; /* * This spinlock protects reporting and other_info, since other_info is usually * required when reporting. */ static DEFINE_SPINLOCK(report_lock); /* * Special rules to skip reporting. */ static bool skip_report(bool is_write, bool value_change, unsigned long top_frame) { if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) && is_write && !value_change) { /* * The access is a write, but the data value did not change. * * We opt-out of this filter for certain functions at request of * maintainers. */ char buf[64]; snprintf(buf, sizeof(buf), "%ps", (void *)top_frame); if (!strnstr(buf, "rcu_", sizeof(buf)) && !strnstr(buf, "_rcu", sizeof(buf)) && !strnstr(buf, "_srcu", sizeof(buf))) return true; } return kcsan_skip_report_debugfs(top_frame); } static inline const char *get_access_type(bool is_write) { return is_write ? "write" : "read"; } /* Return thread description: in task or interrupt. */ static const char *get_thread_desc(int task_id) { if (task_id != -1) { static char buf[32]; /* safe: protected by report_lock */ snprintf(buf, sizeof(buf), "task %i", task_id); return buf; } return "interrupt"; } /* Helper to skip KCSAN-related functions in stack-trace. */ static int get_stack_skipnr(unsigned long stack_entries[], int num_entries) { char buf[64]; int skip = 0; for (; skip < num_entries; ++skip) { snprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]); if (!strnstr(buf, "csan_", sizeof(buf)) && !strnstr(buf, "tsan_", sizeof(buf)) && !strnstr(buf, "_once_size", sizeof(buf))) { break; } } return skip; } /* Compares symbolized strings of addr1 and addr2. */ static int sym_strcmp(void *addr1, void *addr2) { char buf1[64]; char buf2[64]; snprintf(buf1, sizeof(buf1), "%pS", addr1); snprintf(buf2, sizeof(buf2), "%pS", addr2); return strncmp(buf1, buf2, sizeof(buf1)); } /* * Returns true if a report was generated, false otherwise. */ static bool print_report(const volatile void *ptr, size_t size, bool is_write, bool value_change, int cpu_id, enum kcsan_report_type type) { unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 }; int num_stack_entries = stack_trace_save(stack_entries, NUM_STACK_ENTRIES, 1); int skipnr = get_stack_skipnr(stack_entries, num_stack_entries); int other_skipnr; /* * Must check report filter rules before starting to print. */ if (skip_report(is_write, true, stack_entries[skipnr])) return false; if (type == KCSAN_REPORT_RACE_SIGNAL) { other_skipnr = get_stack_skipnr(other_info.stack_entries, other_info.num_stack_entries); /* @value_change is only known for the other thread */ if (skip_report(other_info.is_write, value_change, other_info.stack_entries[other_skipnr])) return false; } /* Print report header. */ pr_err("==================================================================\n"); switch (type) { case KCSAN_REPORT_RACE_SIGNAL: { void *this_fn = (void *)stack_entries[skipnr]; void *other_fn = (void *)other_info.stack_entries[other_skipnr]; int cmp; /* * Order functions lexographically for consistent bug titles. * Do not print offset of functions to keep title short. */ cmp = sym_strcmp(other_fn, this_fn); pr_err("BUG: KCSAN: data-race in %ps / %ps\n", cmp < 0 ? other_fn : this_fn, cmp < 0 ? this_fn : other_fn); } break; case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN: pr_err("BUG: KCSAN: data-race in %pS\n", (void *)stack_entries[skipnr]); break; default: BUG(); } pr_err("\n"); /* Print information about the racing accesses. */ switch (type) { case KCSAN_REPORT_RACE_SIGNAL: pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n", get_access_type(other_info.is_write), other_info.ptr, other_info.size, get_thread_desc(other_info.task_pid), other_info.cpu_id); /* Print the other thread's stack trace. */ stack_trace_print(other_info.stack_entries + other_skipnr, other_info.num_stack_entries - other_skipnr, 0); pr_err("\n"); pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n", get_access_type(is_write), ptr, size, get_thread_desc(in_task() ? task_pid_nr(current) : -1), cpu_id); break; case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN: pr_err("race at unknown origin, with %s to 0x%px of %zu bytes by %s on cpu %i:\n", get_access_type(is_write), ptr, size, get_thread_desc(in_task() ? task_pid_nr(current) : -1), cpu_id); break; default: BUG(); } /* Print stack trace of this thread. */ stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0); /* Print report footer. */ pr_err("\n"); pr_err("Reported by Kernel Concurrency Sanitizer on:\n"); dump_stack_print_info(KERN_DEFAULT); pr_err("==================================================================\n"); return true; } static void release_report(unsigned long *flags, enum kcsan_report_type type) { if (type == KCSAN_REPORT_RACE_SIGNAL) other_info.ptr = NULL; /* mark for reuse */ spin_unlock_irqrestore(&report_lock, *flags); } /* * Depending on the report type either sets other_info and returns false, or * acquires the matching other_info and returns true. If other_info is not * required for the report type, simply acquires report_lock and returns true. */ static bool prepare_report(unsigned long *flags, const volatile void *ptr, size_t size, bool is_write, int cpu_id, enum kcsan_report_type type) { if (type != KCSAN_REPORT_CONSUMED_WATCHPOINT && type != KCSAN_REPORT_RACE_SIGNAL) { /* other_info not required; just acquire report_lock */ spin_lock_irqsave(&report_lock, *flags); return true; } retry: spin_lock_irqsave(&report_lock, *flags); switch (type) { case KCSAN_REPORT_CONSUMED_WATCHPOINT: if (other_info.ptr != NULL) break; /* still in use, retry */ other_info.ptr = ptr; other_info.size = size; other_info.is_write = is_write; other_info.task_pid = in_task() ? task_pid_nr(current) : -1; other_info.cpu_id = cpu_id; other_info.num_stack_entries = stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1); spin_unlock_irqrestore(&report_lock, *flags); /* * The other thread will print the summary; other_info may now * be consumed. */ return false; case KCSAN_REPORT_RACE_SIGNAL: if (other_info.ptr == NULL) break; /* no data available yet, retry */ /* * First check if this is the other_info we are expecting, i.e. * matches based on how watchpoint was encoded. */ if (!matching_access((unsigned long)other_info.ptr & WATCHPOINT_ADDR_MASK, other_info.size, (unsigned long)ptr & WATCHPOINT_ADDR_MASK, size)) break; /* mismatching watchpoint, retry */ if (!matching_access((unsigned long)other_info.ptr, other_info.size, (unsigned long)ptr, size)) { /* * If the actual accesses to not match, this was a false * positive due to watchpoint encoding. */ kcsan_counter_inc( KCSAN_COUNTER_ENCODING_FALSE_POSITIVES); /* discard this other_info */ release_report(flags, KCSAN_REPORT_RACE_SIGNAL); return false; } /* * Matching & usable access in other_info: keep other_info_lock * locked, as this thread consumes it to print the full report; * unlocked in release_report. */ return true; default: BUG(); } spin_unlock_irqrestore(&report_lock, *flags); goto retry; } void kcsan_report(const volatile void *ptr, size_t size, bool is_write, bool value_change, int cpu_id, enum kcsan_report_type type) { unsigned long flags = 0; kcsan_disable_current(); if (prepare_report(&flags, ptr, size, is_write, cpu_id, type)) { if (print_report(ptr, size, is_write, value_change, cpu_id, type) && panic_on_warn) panic("panic_on_warn set ...\n"); release_report(&flags, type); } kcsan_enable_current(); }